assistant2: Add stray visual adjustments (#22111)

Mostly minor tweaks to make it closer to the prototype. More to come.

| With message | Empty state |
|--------|--------|
| <img width="1420" alt="Screenshot 2024-12-16 at 18 59 40"
src="https://github.com/user-attachments/assets/5df791bf-577a-4f01-9045-80568604099f"
/> | <img width="1420" alt="Screenshot 2024-12-16 at 18 59 33"
src="https://github.com/user-attachments/assets/adbf1673-3040-4b2b-8d65-f8b38a83c1d0"
/> |

Release Notes:

- N/A

assets/icons/message_circle.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="lucide lucide-message-circle-more"><path d="M7.9 20A9 9 0 1 0 4 16.1L2 22Z"/><path d="M8 12h.01"/><path d="M12 12h.01"/><path d="M16 12h.01"/></svg>

assets/icons/person.svg

@@ -1,3 +1,4 @@
-<svg width="15" height="15" viewBox="0 0 15 15" fill="none" xmlns="http://www.w3.org/2000/svg">
-<path fill-rule="evenodd" clip-rule="evenodd" d="M7.5 0.875C5.49797 0.875 3.875 2.49797 3.875 4.5C3.875 6.15288 4.98124 7.54738 6.49373 7.98351C5.2997 8.12901 4.27557 8.55134 3.50407 9.31167C2.52216 10.2794 2.02502 11.72 2.02502 13.5999C2.02502 13.8623 2.23769 14.0749 2.50002 14.0749C2.76236 14.0749 2.97502 13.8623 2.97502 13.5999C2.97502 11.8799 3.42786 10.7206 4.17091 9.9883C4.91536 9.25463 6.02674 8.87499 7.49995 8.87499C8.97317 8.87499 10.0846 9.25463 10.8291 9.98831C11.5721 10.7206 12.025 11.8799 12.025 13.5999C12.025 13.8623 12.2376 14.0749 12.5 14.0749C12.7623 14.075 12.975 13.8623 12.975 13.6C12.975 11.72 12.4778 10.2794 11.4959 9.31166C10.7244 8.55135 9.70025 8.12903 8.50625 7.98352C10.0187 7.5474 11.125 6.15289 11.125 4.5C11.125 2.49797 9.50203 0.875 7.5 0.875ZM4.825 4.5C4.825 3.02264 6.02264 1.825 7.5 1.825C8.97736 1.825 10.175 3.02264 10.175 4.5C10.175 5.97736 8.97736 7.175 7.5 7.175C6.02264 7.175 4.825 5.97736 4.825 4.5Z" fill="black"/>
+<svg width="16" height="16" viewBox="0 0 16 16" fill="none" xmlns="http://www.w3.org/2000/svg">
+<path d="M12.6666 14V12.6667C12.6666 11.9594 12.3856 11.2811 11.8855 10.781C11.3854 10.281 10.7072 10 9.99992 10H5.99992C5.29267 10 4.6144 10.281 4.1143 10.781C3.6142 11.2811 3.33325 11.9594 3.33325 12.6667V14" stroke="black" stroke-width="1.33333" stroke-linecap="round" stroke-linejoin="round"/>
+<path d="M7.99992 7.33333C9.47268 7.33333 10.6666 6.13943 10.6666 4.66667C10.6666 3.19391 9.47268 2 7.99992 2C6.52716 2 5.33325 3.19391 5.33325 4.66667C5.33325 6.13943 6.52716 7.33333 7.99992 7.33333Z" stroke="black" stroke-width="1.33333" stroke-linecap="round" stroke-linejoin="round"/>
 </svg>